1. Field of the Inventions
The present application relates to a method of and system for steering a watercraft propulsion device.
2. Description of Related Art
Conventionally, cable and hydraulic manual steering systems are used for steering watercraft propulsion devices such as outboard motors and stem drives (hereinafter “outboard motors”). The cable-type steering systems can generate high operational loads. Thus, the hydraulic manual steering systems are more commonly used.
In hydraulic manual steering systems, it is not practicable to include control systems for optimizing steering angles in accordance with watercraft speed. In addition, since hydraulic piping is required for such systems, additional space for the piping is required in the hull. Thus, the design of the system structure is complicated and construction and servicing are time-consuming.
More recently, a “Drive-By-Wire” (DBW) type system has been developed in which steering is electronically controlled using a steering drive unit including an electric motor (see Japanese Patent Publication No. Hei 4-38297, for example). In this system, an outboard motor is mounted to a transom plate and includes a steering drive unit having an electric motor which drives the outboard motor to rotate about a swivel shaft. The method of operating the system includes calculating a control quantity for the steering drive unit in accordance with the degree of operator's steering displacement, and operating the steering drive unit based on the calculated control quantity.
In such conventional method of steering an outboard motor, a control quantity can be directly and unequivocally correlated to the steering wheel displacement. The control command signal, based on the steering angle as the control quantity, is sent to the steering drive unit to control the electric motor so as to maintain the steering drive unit in the desired orientation.